Carbon Material Activation Equipment and Method

ABSTRACT

The present invention of a carbon material activation equipment and method is advantageous in that since a carbon material used for electric process does not have to be an electrode shape, it is possible to separate the activated carbon material from a reactor free from damage to the activated carbon material after the electric process. A carbon material activation equipment according to the present invention comprises a reactor  12  to be filled with a particulate carbon material, an insulating container  10  with said reactor  12  placed therein, an electrolyte  18  to fill said insulating container  10  and said reactor  12 , a counter electrode  14  placed under said reactor  12  in said insulating container  10 , and a voltage applying means  22  to apply a voltage to said reactor  12 , a working electrode, and said counter electrode  14.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a carbon material activation equipment and method, and an electric double layer capacitor (EDLC) thereof, wherein a carbon material is used as a polarizable electrode in an EDLC.

2. Background of the Related Art

An EDLC is a kind of condensers, which charges or discharges electricity by adsorption/desorption of ions on or from the surface of an electrode composed of a porous conductive material. A porous carbon material such as high-surface-area activated carbon is generally used for adsorption of ions on the surface of an electrode as a porous conductive material.

An EDLC has been commercialized as permanent power and energy backup source for microelectronic devices, and is recently considered to be used as a power source for hybrid electric vehicles (HEV). For the use in HEV, it requires high-performance and high-capacity per unit volume and weight.

Various suggestions on a porous carbon material used for an electrode have been made to meet the requirement of high-performance. Most of all, various methods of using high-surface-area activated carbon are suggested for increasing the surface area of electrodes in order to achieve high-capacity per unit volume.

For example, a method of making use of an activated carbon with high surface area of 3000˜4500 m2/g depending on activation of alkali for an electrode, wherein the method uses an excess alkali hydroxide, is suggested. An electrode obtained by this method, however, causes to lower the bulk density and the capacitance per unit volume of an EDLC. Besides, even though the surface area of an electrode increases, it is often for the capacitance of the EDLC not to increase in proportion thereto. In addition, an alkali activation method using an excess alkali hydroxide has problems of corrosion of reactor or high reaction of by-product alkali metal, thereby imposing a burden to industrial productivity.

Another suggestion is a composite electrode with a carbon forming an ion dissociative functional group such as a sulfonate group and a conductive polymer. This is an attempt to increase gross capacitance by adding pseudo-capacitance through oxidation-reduction of surface functional group which is combined to the surface of an electrode. This, however, has a problem of performance degradation of an EDLC caused by increasing of leakage current when maintaining the charged state through a side reaction of repeated charge-discharge.

Meanwhile, still another suggestion of electric field activation method has introduced that improves capacitance by forming a capacitor cell by use of a porous carbon and generating a high electric field in an electrode through applying over-voltage when first applying voltage, which forms small pores by making ions penetrate through the porous carbon.

FIG. 1 illustrates a representative conventional electric activation device. After installing discharge electrodes 1, 2 composed of a carbon solid, it is to discharge electricity by applying a voltage to the electrodes 1, 2 through power source 5. The container 3 is an insulating container, and one of discharge electrodes 2 is in the lower part of the container 3, which is filled with an electrolyte 4. A sample 6 is a carbon sheet shaped 20 mm in diameter and 1 mm in thickness, installed at a fore-end of the other discharge electrode 1, and dipped in said electrolyte 4.

Since a conventional electric activation device makes use of an above said carbon solid as a sample, it is necessary to separate and take out the carbon sheet from a discharge electrode or a separator after the electric activation process ends. At this point, there arise problems in that as the surface of the carbon sheet becomes flexible because of an electrolyte, the carbon sheet electrically activated from the discharge electrode or a separator can be ruined or damaged, thereby making the carbon sheet unusable or causing capacitance dispersion of the EDLC. Another problem is that the process to arrange the carbon sheet with the surface made flexible in a wrap sheet gets complicated.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made in view of the above problems occurring in the prior art, and it is an object of the present invention to provide a carbon material activation equipment, a carbon material activation method, and an EDLC thereof, which is free from the above problems.

The above object of the present invention can be achieved by a carbon material activation equipment comprising a reactor 12 to be filled with a particulate carbon material; an insulating container 10 with said reactor 12 placed therein; an electrolyte 18 to fill said insulating container 10 and said reactor 12; a counter electrode 14 placed under said reactor 12 in said insulating container 10; and a voltage applying means 22 to apply a voltage to said reactor 12, a working electrode, and said counter electrode 14.

The above object of the present invention can also be achieved by a carbon material activation method comprising steps of filling a particulate carbon material in a reactor 12 in an insulating container 10 filled with an electrolyte; and electrically activating by applying a voltage to said reactor 12, a working electrode, and a counter electrode 14 which is placed under said reactor 12.

The present invention of a carbon material activation equipment and method is preferable to further comprise a reference electrode 16 in an insulating container 10.

In the present invention of a carbon material activation equipment and method, it is preferable for a reactor 12 to have a plurality of pores 20 which pass an electrolyte 18, but not a particulate carbon material therethrough.

The above object of the present invention can also be achieved by an EDLC which makes use of an activated carbon material as an electrode, wherein the carbon material is activated by said carbon material activation equipment and said carbon material activation method, and then formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a carbon material activation equipment according to a prior art;

FIG. 2 is a perspective view of a carbon material activation equipment according to the present invention;

FIG. 3 illustrates waveforms of voltages generated in the voltage applying means of a carbon material activation equipment according to the present invention; and

FIG. 4 is a sectional view of an EDLC using a carbon material which is activated according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention of a carbon material activation equipment, a carbon material activation method, and an EDLC fabrication method will now be described in detail in connection with specific embodiments with reference to the accompanying drawings.

FIG. 2 shows a carbon material activation equipment and a carbon material activation method according to the present invention. A reactor 12 containing a carbon material is composed of a conductive material, and dipped by half in an electrolyte 18 which fills an insulating container 10. Such a reactor 12 operates as a working electrode (or a counter electrode 14) in the present invention. In the insulating container 10 is placed a carbon solid electrode working as a counter electrode 14 (or a working electrode) under the reactor 12. A plurality of pores 20 can be formed in the reactor 12, therethrough an electrolyte 18 can pass, but a particulate carbon material can not pass. At this point, the outer side of the reactor 12 can be covered with an insulator depending on an activation method.

The present invention of a carbon material activation equipment can install a reference electrode 16 in the insulating container 10: in case that the present invention of a carbon material activation equipment uses a non-aqueous electrolyte, it is preferable to use non-aqueous Ag/Ag+ as the reference electrode; otherwise in case of using an aqueous electrolyte, it is preferable to use aqueous Ag/Ag+, Hg/HgO, or SCE (Saturated Calomel reference electrode) as the reference electrode. Such a reference electrode 16 can be placed either outside the reactor as shown in FIG. 2, or inside the reactor.

The insulating container 10 and the reactor 12 are filled with an electrolyte 18, which can be a carbonate based material such as non-aqueous polycarbonate (PC), ethylene carbonate (EC), and sulfolane; or an aqueous sulfuric acid solution, an aqueous nitric acid solution, or an aqueous basic solution such as potassium hydroxide (KOH). It is preferable to use a carbon solid for the reactor 12, yet precious metal container, which is safe for leaching by an electrolytic reaction, can also be used therefor. In case that metal materials are used, discharge sputtering trail of the metal component may be intermixed with the activated carbon material. Besides, as shown in FIG. 2, two or more reactors 12, not only one, can be installed. If the reactor 12 gets too big, the carbon material in the center can not be activated sufficiently. Therefore, it is preferable to limit the size of the reactor 12 in a certain range, and install several reactors 12 in order to increase the amount of the carbon material treated in one process.

The present invention of a carbon material activation equipment can electrically activate a particulate carbon material. Therefore, it is not necessary to form a carbon material into an electrode shape before the treatment, but the carbon material can be used as it is. This includes an activated carbon which is activated by other methods, a non-activated carbon compound, or a mixture thereof.

A carbon material activation method according to the present invention is to put a particulate carbon material into the reactor 12 of an activation equipment, and apply a voltage to both the reactor 12 as a working electrode and the counter electrode 14 by a voltage applying means 22. The voltage applied by the voltage applying means 22 can be a square wave voltage shown in FIG. 3( a), an alternating voltage as shown in FIG. 3( b) or FIG. 3( c), or an alternating voltage with two or more waveforms combined as shown in FIG. 3( d). At this point, it is preferable that the applied voltage is more than the reference electrode 16 as a standard hydrogen electrode (SHE) by 2 V or more in about over π period; or more than the reference electrode 16 as a standard hydrogen electrode (SHE) by 0 V or less.

Embodiment

An embodiment of the present invention will now be described in detail. In an embodiment of the present invention, DC power of 10˜100 V is used; a glass container is employed as an insulating container 10; and an aqueous sulfuric acid solution is taken as an electrolyte 18. The reactor 12 is set to be dipped in the electrolyte 18 by half.

A carbon material is prepared as a powder with a thermoplastic resin which is heated in the range over the temperature at which the resin melts or the endothermic reaction accompanying the melting thereof stops, and below the temperature at which the oxidation starts; and the thermoplastic resin is cooled down to room temperature to be made into powder.

The reactor 12 is to be filled with the carbon material by a third (⅓), and a voltage of 60 V is to be applied to the working electrode and the counter electrode 14 by a DC power supply means, resulting in flowing electric current of 3 A. After applying the voltage, gas is generated around the carbon material. That is because the electrolyte 18 around the carbon material is electrolyzed.

The generated gas covers each particle of the carbon material for the carbon material and the electrolyte 18 to be momentarily insulated, and the voltage gets higher. When the voltage gets high, it starts to discharge in the insulating layer formed by the gas generated in the reactor 12. As the result, the gas becomes ion gas and a part of the surface of the carbon material comes to be heated. The carbon material is activated by the heat and the ion gas. After starting of the discharge, the voltage grows falling; and the discharge in turn stops. This process of electric discharge is repeated a plurality of times, thereby activating the carbon material.

Besides, a carbon material activation can be achieved by applying an alternating voltage to the reactor 12 and the counter electrode 14 in order for ions and a solvent to repeat electrochemical intercalation/de-intercalation behavior in layer structure of the carbon material. In this case, it is preferable to apply a square wave voltage or an alternating voltage with shorter period than that in case of the activation by electric discharge.

In this embodiment, a resin is used as a carbon material. Apart from that, it is possible to use an activated carbon which is activated by other methods, a non-activated carbon compound, or a mixture thereof.

In order to fabricate a polarizable electrode for an EDLC by use of the activated carbon obtained by the present invention of a carbon material activation method, a conventional method can be employed. For example, a material on the market, known as a binder, such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), etc. can be formed to be an electrode by being added by a few % as needed, fully mixed, put in a mold to be press-formed or rolled to be a sheet, and punched into a desired shape. At this point, a solvent such as organic compounds like alcohol and N-methylpyrrolidone (NMP), and water, a dispersing agent, and various additives can be used as needed. Heat can be added as well.

It is necessary to consider the temperature condition because higher temperature than necessary affects not only degradation of the employed binder ingredient, but also properties relevant to the surface structure of an activated carbon such as a surface area.

By adding a conductive material like a conductive carbon such as carbon black, Ketjenblack EC when forming an electrode, the resistance of the electrode can be lowered. This is effective for decreasing the internal resistance of a polarizable electrode, and making the volume of the electrode small. In addition to a sheet electrode described above, a coated electrode can be employed which is made by coating a collector with the mixed material.

A polarizable electrode described above is useful for an electrode of an EDLC shown in FIG. 4.

Other elements of an EDLC of FIG. 4 than the polarizable electrode shown above are the same with those of a well-known conventional EDLC. In other words, elements 40, 42 are current collector members composed of aluminum; elements 44, 46 are polarizable electrodes composed of an activated carbon of the present invention; an element 48 is a separator composed of polypropylene non-woven fabric; an element 50 is a gasket composed of any one of polypropylene (PP), polyethylene (PE), polyamide (PA), polyamide imide (PAI), polybutylene (PB), and the like; and an element 52 is a cover and case composed of a material like stainless.

Besides, in order to operate an EDLC, it is necessary to seal an electrolyte dissolved in a solvent in the case 52: the electrolyte can be any one of a group consisting of tetraethylammonium tetrafluoroborate, tetramethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, and so on; and the solvent can be ethers such as tetrahydrofuran (THF), carbonates such as dimethyl carbonate (DMA), diethyl carbonate (DEC), ethylene carbonate (EC), and propylene carbonate (PC), nitriles such as acetonitrile, lactones such as γ-butyrolactone, and α-methyl-γ-butyrolactone, sulfoxides such as dimethyl sulfoxide (DMSO), and amides such as dimethylformamide (DMF).

Since an EDLC with the elements illustrated in FIG. 4 adopts an activated carbon according to the present invention, it shows high self discharge maintenance rate.

The present invention of a carbon material activation equipment and method is advantageous in that, since a carbon material used for electric process does not have to be an electrode shape, it is possible to separate the activated carbon material from a reactor free from damage to the activated carbon material after the electric process. Another advantageous effect is that, as the carbon material is shaped after activation process, it is possible to be shaped variously depending on the application. 

1. A carbon material activation equipment comprising: an insulating container which is to be filled with a electrolyte; a reactor which is to be filled with particulate carbon material and placed in said insulating container; an electrode which is placed under said reactor in said insulating container; and a voltage applying means which applies a voltage to said reactor and a counter electrode, wherein said reactor is used as a working electrode and said electrode as the counter electrode.
 2. The carbon material activation equipment of claim 1, further comprising a reference electrode in said insulating container.
 3. The carbon material activation equipment of claim 2, wherein said reference electrode comprises any one of a group consisting of non-aqueous Ag/Ag+, aqueous Ag/Ag+, Hg/HgO, and SCE.
 4. The carbon material activation equipment of claim 2, wherein said voltage applying means applies more voltage than said reference electrode by 2V or more.
 5. The carbon material activation equipment of claim 2, wherein said voltage applying means applies more voltage than said reference electrode by 0 V or less.
 6. The carbon material activation equipment of claim 1, wherein said electrolyte comprises any one of a group consisting of carbonate based material such as non-aqueous polycarbonate (PC), ethylene carbonate (EC), and sulfolane.
 7. The carbon material activation equipment of claim 1, wherein said electrolyte comprises any one of a group consisting of an aqueous sulfuric acid solution, an aqueous nitric acid solution, or aqueous basic solution.
 8. The carbon material activation equipment of claim 1, wherein said voltage applying means applies a square wave voltage or an alternating voltage.
 9. The carbon material activation equipment of claim 1, wherein said reactor has a plurality of pores which pass an electrolyte, but not a particulate carbon material therethrough.
 10. The carbon material activation equipment of any one of claims 1 to 9, said reactor can be plural.
 11. A carbon material activation method comprising steps of: applying a voltage to a working electrode and a counter electrode, wherein a reactor dipped in an electrolyte is used as the working electrode and an electrode placed under said reactor as the counter electrode; and activating a particulate carbon material contained in said reactor.
 12. The carbon material activation method of claim 11, wherein said electrolyte comprises any one of a group consisting of carbonate based material such as non-aqueous polycarbonate (PC), ethylene carbonate (EC), and sulfolane.
 13. The carbon material activation method of claim 11, wherein said electrolyte comprises any one of a group consisting of an aqueous sulfuric acid solution, an aqueous nitric acid solution, or aqueous basic solution.
 14. The carbon material activation method of claim 11, wherein said voltage applied to said working electrode and said counter electrode is a square wave voltage or an alternating voltage.
 15. The carbon material activation method of claim 11, wherein said voltage applied to said working electrode and said counter electrode is more than a reference electrode, a standard hydrogen electrode, by 2V or more.
 16. The carbon material activation method of claim 11, wherein said voltage applied to said working electrode and said counter electrode is more than a reference electrode, a standard hydrogen electrode, by 0 V or less. 